1. Field of the Disclosure
Embodiments of the present invention generally relate to substantially surfactant-free submicron hydrophobic agent dispersions with high levels of water miscible solvent.
2. Description of Related Art
The current practices for combining a hydrophobic material (such as liquid, semi-solid, or solid) with a hydrophilic liquid requires the addition of agents that change the native properties of both the hydrophobic material and the hydrophilic liquids so that they more closely resemble one another. As the properties of the two phases converge because of the additives, they have a greater propensity to be stable for a commercially viable period of time. An important class of additives that can be used in these hydrophobic phase/hydrophilic phase combinations is the surface-active agent, which is typically referred to as a “surfactant”. These surfactants have both hydrophobic and hydrophilic properties.
When one or more of these agents are incorporated into the hydrophobic phase, the hydrophilic phase, or both the agents will align themselves at the hydrophobic phase-hydrophilic phase interface or at the interface between the composition and the surrounding air. The force that exists at the hydrophobic phase-hydrophilic phase (“Interfacial Tension”) is reduced, allowing the two phases to more favorably coexist. Similarly, the force that exists at the air-composition interface (“Surface Tension”) is also reduced. A special sub-category of “surfactants” is called an emulsifier. When carefully selected, such emulsifiers have a wide range of surface-active properties. These materials not only lower the interfacial tension at the hydrophobic phase-hydrophilic phase interface but, with the input of shearing energy, they enable the formation of stable droplets of one phase within the other. The resulting product is called an emulsion. In many cases such emulsions are prepared by heating the hydrophobic and hydrophilic phases to a temperature of 70° C. or greater before combining the two phases. The purpose of heating the phases is to ensure that all semi-solid and solid hydrophobic materials used are melted, and that the two phases have a low enough viscosity so the two phases can mix freely. The hydrophobic and hydrophilic phases are typically mixed together until they achieve a homogeneous appearance. Thereafter, they are cooled to ensure the formation of appropriately sized droplets, which is usually on average in the 3 micron to 10 micron range. Such emulsions typically have a homogeneous, opaque, white appearance due to their particle size.
These emulsions present difficulties in that the processing that creates stable emulsions is difficult to scale from the laboratory to production, and they are not amenable to maintaining emulsion stability upon dilution. Moreover, the stability of these emulsions is particularly problematic when the hydrophilic phase contains significant amounts of a water-miscible solvent.